First of all: You have defined your whole table content inside a thead element?
If you inspect the header cells to see why they are bold you will see that the bold font-weight comes from a rule in the user agent stylesheet for the th element. So by default thead and tfoot have nothing to do with the font weight.
If you compare your markup in the tfoot element with Mosh’s you will see that he uses th elements while you are using td elements. That’s why your table looks different.
BTW: In my opinion wrapping a data value with a th is not correct sematically. I would write